Numerous radio frequency (RF) signal sources are currently available for supplying television signals to a user's television receiver. These RF signal sources include, an ultra-high frequency (UHF) antenna, a very-high frequency (VHF) antenna, video games, home computers, cable television systems, videocassette recorders, videodisc players, and TVRO (television receive-only) satellite television receivers.
Many modern television receivers are equipped with multiple RF signal input connectors, and have the capability of receiving video signals from two different RF signal sources. A television receiver with two RF signal input terminals eliminates repeated plugging-in and unplugging of cables which would otherwise be necessary when changing from one signal source to another.
Systems which allow a user to enter a list of preferred channels (i.e., a scan list) of those channels which are receivable via an RF input terminal, are known. Such scan lists include information as to whether or not the desired channel is an "AIR" channel or a "CABLE" channel, information concerning the tuning voltage required to tune the channel, and information indicating in which band of frequencies the desired channel resides. With such a system, a user can program into the scan list only those channels which are of interest to him, thereby causing the "skipping" of unused, or undesired channels when changing channels via a "channel up", or "channel down" command. Scanning down beyond the last channel stored in the scan list causes the tuning of the first channel in the scan list. Similarly, scanning up beyond the first channel stored in the scan list causes the tuning of the last channel in the scan list. This method of operation is known as "wrapping around" from top to bottom or, bottom to top. Inclusion of a scan list feature in a television receiver having multiple RF input terminals is known from the RCA CTC-133 color television receiver, manufactured by Thomson Consumer Electronics, Inc., Indianapolis, Ind. In this receiver, each RF input terminal has a separate scan list associated with it.
It is common practice for cable television services to remodulate television signals transmitted on given "air" channels, onto different cable channels. For example, the signals of channel 29 may be remodulated on a cable system and appear on cable channel 8. Therefore, with a separate scan list arrangement, the same channels may appear in more than one scan list. Using the previous example, assume RF input terminal A is connected to an external antenna, and RF input terminal B is connected to a cable converter unit. In this arrangement, the signals from a given broadcaster (channel 29) will appear on channel 29 on RF input terminal A., and the same signals will appear on RF input terminal B, on cable channel 8. There are two reasons for wanting to eliminate the above-noted duplication of channels. First, the duplication of channels may be annoying to a user who is scanning through the available channels in both scan lists in sequence. Second, the memory space available for the scan lists is limited, and such duplication is wasteful, especially in light of the fact that a receiver coupled to both cable and satellite systems may have over 100 television channels available for viewing.
A user who deletes an otherwise duplicated channel from one of the scan lists must either remember in which scan list it is to be found, or search through the channels of both scan lists. Searching through the scan lists requires that the user scan through the channels by use of the "channel up" or "channel down" keys until the above-mentioned "wrap-around" of the scan list occurs. This ensures that the user has seen all of the channels of a first scan list before selecting another RF input and scanning through its related scan list for the desired channel. Unfortunately, this method of operation also causes the viewer to see at least one of the channels of the first scan list, a second time in order to be sure that he has indeed seen all of the channels in the first list.
Copending U.S. patent application Ser. No. 589,830 (Keenan) discloses a solution to the above noted problems in that the scan lists associated with each RF input terminal are capable of being linked together so that a user may scan through all channels on all scan lists in sequence, with the proper RF input terminal being automatically selected when the system automatically advances from one scan list to another. It is desirable that the user be informed of which scan list (i.e., which RF input terminal) is currently selected. The above-mentioned RCA CTC-133 color television chassis provides an on-screen display including channel number, and a message A1, A2, or A3 to indicate which RF input terminal is selected. It is felt, however, that such a two line display may be objectionable to some viewers who may feel that it clutters the display screen.